This invention pertains to wireless networks generally, and means for connecting wireless nodes or wireless LANs to wired LANs in particular.
Local Area Networks (LANs) have historically consisted of nodes interconnected by physical telecommunications media (eg, coaxial cable, twisted pair wire, or fiber optics). We shall refer to such LANs as wired LANs.
Recently wireless LANs, the nodes of which are not connected by means of a physical medium, have started to appear in the market. These wireless LANs communicate by means of infra-red (IR), radio or other signals. One of the benefits of using wireless LANs is that cabling is not required. This is a particularly useful feature for mobile nodes such as laptop and notebook computers, PDAs (personal digital assistants), and the like. If appropriately equipped with an appropriate wireless adapter (which includes a transmitter/receiver and control card), such as an IR wireless Adapter, the mobile nodes can move around and remain connected to the network, provided they do not move out of range.
One method of implementing a wireless LAN is similar to a cellular phone network system. In this method wireless nodes do not communicate directly with each other, but rather send all signals to a central base station, which then redirects the signals to the destination node.
However, in certain situations, it is advantageous to allow each wireless node to communicate directly with other nodes, as is the case in most wired LANs. In a wireless LAN which permits this, the wireless adapter and controlling software transmit data packets which all nodes within range can hear. This permits transmitting of packets which are received but ignored by all nodes except the one(s) to which they are addressed. This parallels the packet delivery systems of such wired LAN protocols as Ethernet. Thus, upper level network operating system software, which relies on a packet delivery system such as Novell Corporation""s NETWARE (tm) can be used with such a wireless LAN. We shall refer to such a wireless LAN as a Peer-to-Peer Wireless LAN.
There is an important physical characteristic in a peer-to-peer wireless LAN that makes it very difficult to build a reliable network compared to a wired LAN. In a wired LAN, every network node is physically connected to the network and can therefore access all of the network traffic. This is often not the case with wireless LANs. Each node communicates with other nodes by means of some form of electromagnetic signal, the range of which will be limited. Each node will have an area of coverage which will be limited by such factors as type of signal, signal strength, obstacles within range, etc. In the wireless LAN, it cannot be guaranteed that every network node, which is presumably part of the same wireless network, can listen to all the network traffic. For example, if nodes A, B, and C are connected to the same wireless network, A may be able to listen to the network data sent by B but not by C. In this case, C is a xe2x80x9chidden nodexe2x80x9d with respect to A. If C can listen to B but not to A, then A is a hidden node with respect to C.
For proper functionality, it is desirable that a wireless LAN should also be able to connect to a wired LAN. In wireless LANs using a base station approach, the Base Station can provide such connectivity. However, there exists a need for system which can provide internetworking services between a peer-to-peer wireless LAN and a wired LAN.
There are several problems associated with a wireless LAN which complicate the implementation of a simple bridge as a means for connecting a wireless LAN to a wired LAN. The primary function of such a device would be to resend overheard wireless LAN network data that is destined for a wired node onto the wired LAN, and vice versa. Depending on the wireless medium chosen, each such device would normally have a limited range. In order to provide adequate coverage, a plurality of devices, each having some degree of overlapping area is necessary. This would normally result in the duplication of messages received by nodes within the overlapping areas, and also on the wired LAN for messages originating from such nodes.
There exists a need for a system which solves these and related problems.
In this specification, the following terms are used:
By internetworking services, we refer to services which allow systems to communicate which could not otherwise. Typical internetworking services include relaying messages from one wireless node to another, resending messages from a wired LAN to a wireless node and resending messages from a wireless node to a wired LAN.
The internetworking node that provides such internetworking services is called an Access Point or AP. The AP is a physical device, which, in order to perform the full range of internetworking services has a wired network adapter as well as a wireless network adapter.
The physical area that a wireless node must be within to be within range of the AP is called the AP""s Basic Service Area (BSA). If a wireless node is located within the BSA of a particular AP, that wireless node will be able to receive transmissions sent by that AP.
Each wireless node also has a limited range within which it can communicate. This range is called the Dynamic Service Area (DSA) of the wireless node in this specification. Other nodes within an wireless node""s DSA will normally be able to receive transmissions from the wireless node.
If the wireless nodes use the same adapter as the APs, then, all other things being equal, the wireless nodes will have the same range as the APs. However there can be differences between the BSA range of the AP and the DSA range of a wireless node. For one thing, the wireless nodes are usually movable. Thus their range is likely to change, depending on how their signals are affected by obstacles as they move. Also, access points, being physically connected to a wired LAN, are also connected to a supply of power. Thus, the transmitter used in an AP can be more powerful than the battery powered transmitters of the wireless nodes. If this is the case, the BSA range of an access point would normally be larger than the DSA range of a wireless node.
In this specification, we will distinguish between the BSA of an AP and the DSA of a wireless node, even if the two ranges are the same. In this specification, one wireless node is said to be able to xe2x80x9chearxe2x80x9d a second wireless node if it is within the DSA of the second node, so that signals sent by the second node can be received by it. Similarly, a wireless node can xe2x80x9chearxe2x80x9d an AP if it is within the BSA of the AP, and an AP can xe2x80x9chearxe2x80x9d a wireless node if the AP is within the DSA of that node.
A xe2x80x9cmulticastxe2x80x9d message is a form of broadcast message, sent by a wired or wireless node, which is addressed to other nodes having the same specific group address. All other wired or wireless nodes will ignore that message.
The invention provides a method and a means for providing internetworking services to wireless nodes. The invention provides for an internetworking node which can either directly relay a message from one wireless node to another wireless node, or forward such messages indirectly by first resending them to another such internetworking node which in turn resends the message to the other wireless node. The internetworking devices themselves can communicate through the wireless medium. Preferably, such internetworking devices are interconnected by means of a wired LAN.
From a user""s point of view, the invention makes such wireless nodes, as for example from a wireless LAN, and a wired LAN appear as a single logical LAN. The invention allows for integration of wireless nodes with existing wired LAN based network operating systems and network applications, by making each wireless node appear as wired network nodes to other wired network nodes when a wireless node sends data packets to a wired network node. Similarly, where a wireless node is part of a wireless LAN, the invention makes a wired network node appears as a wireless node to other wireless nodes when the wired network node sends data packets to the wireless node.
The invention provides a method and means for using one or more APs as internetworking devices which interconnect a wired LAN and wireless nodes within range of each AP, and for determining when each AP should act to transmit data between the wired LAN and wireless nodes.
The primary functions for each AP are, when appropriate, i) to resend data packets from a wireless node onto the wired LAN if the data packets cannot otherwise reach their destination (eg, if they are destined for a wired node, or are destined for a wireless node outside of the DSA of the sending node); and ii) to resend data packets, which are addressed to a wireless node, from the wired LAN to the wireless node. In the preferred embodiment, the wireless node is part of a wireless LAN. The AP, having both a wired network adapter as well as a wireless network adapter, can communicate using both the packet delivery system of the wired medium, as well as the packet delivery system of the wireless medium. Furthermore, the AP is able to convert a data packet from one system to the other.
Preferably, the APs will also redirect information between two wireless nodes which are both within the AP""s range, but are hidden to each other. The invention allows for this even if the AP is not connected to a wired LAN.
To achieve these functions each AP has to know whether the data packets are for a destination within its own BSA, and whether it is responsible for acting. The wireless nodes use a process of association with at most one of the APs to carry out these functions. Each wireless node within range of at least one AP will associate itself with a single AP, even if it is within range of more than one AP. Once a wireless node associates itself with an AP, it will use that AP, and only that AP, to forward data to and from the wireless node. The AP keeps track of which nodes are associated with it, in order to determine whether it is responsible for acting.
Each wireless node monitors the wireless network traffic, and keeps track of which nodes are within its range, ie, which other wireless nodes it has overheard recently. According to the invention, each wireless node uses this information to determine which wireless nodes, including APs, are within its range.
Preferably, each AP broadcasts information about itself at regular intervals. In the preferred embodiment, this broadcast is in the form of a beacon identifying its network address. Each wireless node can determine, from either the AP""s regular data transmissions, or from this beacon, whether it is within the AP""s BSA. The wireless node keeps track of APs it has overheard. Preferably the node maintains a table of APs it has overheard recently.
If the wireless node overhears data packets (either normal traffic or a beacon) from an AP, it can attempt to associate with the AP by sending an association request to the AP. If a wireless node""s association request fails, it will preferably attempt to associate with another AP currently in its AP table. If the wireless node overhears more than one AP, or there is more than one AP in its table, the wireless node determines which AP it will select. In one embodiment, the mobile node selects the AP it has heard most recently.
When a wireless node (the sending node) needs to send a data packet to a particular node (destination node), it first checks to see if it has recently overheard the destination node (implying the destination is within range). Optionally, each wireless node can emit a beacon to assist the other nodes in this.
If the destination node is within range, the sending node transmits the data packet directly to the destination node. If the sending node has not recently overheard the destination node, the sending node checks to see whether it is associated with an AP. Assuming the sending node is associated with an AP, the node transmits the packet to the AP and asks the AP to forward the data packet to its destination.
Once an AP has received a request from a sending node, which it is associated with, to forward a data packet, the AP will check to see if the destination node is also associated with this AP. If so, the AP will transmit the data packet directly to the destination node. If not, the AP will resend the data packet, which is still addressed to the destination node, onto the wired network.
Whenever an AP overhears a directed packet on the wired LAN addressed to a wireless node, the AP checks to see if that node is associated with it. If so, the AP will forward the data packet to the node. Otherwise, the AP will ignore the packet. Similarly, whenever an AP overhears a broadcast packet on the wired LAN, it retransmits the packet to all wireless nodes associated with it.
Thus, in the preferred embodiment, each wireless node actively selects which AP it is associated with, and determines whether it needs an AP""s help to send messages. Each AP keeps track of which wireless nodes are associated with it, and automatically relays data packets addressed to associated nodes which the AP has received, either from the wired LAN, or from another associated wireless node.
A broad aspect of the invention provides for a node for communication in a network, comprising wireless network adapter means for sending data by wireless communication to other nodes in the network and receiving data by wireless communication from such nodes, monitoring means for monitoring data which are received by said wireless adapter means, to extract from said data identifying information which identifies the other network nodes whose data are received, and storage means for storing the identifying information.
Another broad aspect of the invention provides for a method for communication in a network, comprising sending data by wireless communication from a first node in the network to other nodes in the network and receiving data by wireless communication from such nodes, monitoring data which are received to extract from said data identifying information which identifies the other network nodes whose data are received, and storing the identifying information.
These foregoing aspects of the invention, together with other aspects and advantages thereof will be more apparent from the following description of the preferred embodiments thereof, taken in conjunction with the following drawings.